Introduce GetWebExposedScrollOffsets for scrollingAPIs

We have encountered the issue where simply changing zoom levels can lead to unexpected scrolling on our sample page. This is due to updating of truncated scroll offset [1] when FractionalScrollOffset is disabled, which led to a loss of fractional precision, resulting in a 1px discrepancy at the webAPI level. To ensure compatibility with web standards while preserving the integrity of scroll offsets, this commit introduces GetWebExposedScrollOffsets for scrollingAPIs (e.g. Element.scrollTop, Element.scrollLeft, window.scrollX, window.scrollY). Also by enabling FractionalScrollOffsets, we can address underlying issue of scroll offset truncation. [1] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/scroll/scrollable_area.cc;drc=43e12b162c85779c8350871dac4b319cc1874f16;l=671 Bug: 326122314 Change-Id: I070be67b0e73d925738d556ff0626e6a1119ff00 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5348560 Commit-Queue: Minju Kim <mkim@igalia.com> Reviewed-by: David Bokan <bokan@chromium.org> Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org> Reviewed-by: Steve Kobes <skobes@chromium.org> Cr-Commit-Position: refs/heads/main@{#1288468}
web-platform-tests · Apr 17, 2024 · 228b075 · 228b075
1 parent b8a81e1
commit 228b075
Showing 1 changed file with 35 additions and 0 deletions.
diff --git a/css/css-viewport/zoom/scroll-top-test-with-zoom.html b/css/css-viewport/zoom/scroll-top-test-with-zoom.html
@@ -0,0 +1,35 @@
+<!doctype html>
+<title>Scroll Top Test with Zoom</title>
+<link rel="help" href="https://drafts.csswg.org/css-viewport/#zoom-property">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+  #container {
+    width: 200px;
+    height: 100px;
+    border: solid thick;
+    overflow: auto;
+  }
+</style>
+<div id="container">
+  <div style="width: 100px; height: 2000px"></div>
+</div>
+
+<script>
+  var container = document.getElementById('container');
+  container.scrollTop = 77;
+  test(function() {
+    assert_equals(container.scrollTop, 77, "Initial scrollTop should be 77");
+  }, "Initial scrollTop with no zoom");
+
+  document.body.style.zoom = 1.2;
+  test(function() {
+    assert_approx_equals(container.scrollTop, 77, 0.99, "scrollTop should remain consistent within 1 px after zooming in");
+  }, "scrollTop after increasing zoom level");
+
+  document.body.style.zoom = 1;
+  test(function() {
+    assert_equals(container.scrollTop, 77, "scrollTop should remain consistent after resetting zoom");
+  }, "scrollTop after resetting zoom");
+  done();
+</script>